**1. Introduction**

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As long as any country economy is based on fossil fuels, the prosperity of many nations is in danger. Rapidly growing prices of oil and natural gas can lead to the worldwide economic crisis. Therefore the search for new, clean, cheap and renewable sources of energy and energy carriers is urgently required. Although many different methods are suggested to solve this problem the use of hydrogen as the future energy carrier is necessary. Application of biochemistry in generation of energy is a challenge both for academia and industry. Different types of biomass pyrolysis and/or fermentative processes can partially solve the problems of renewable energy generation. Although other solutions are at the moment much more technologically advanced (e.g. hydropower or wind farms) the future of energetic will belong to the biological systems. Generation of biogas or biohydrogen under anaerobic conditions are the very promising processes, especially at local environment. Different types of agriculture and food industry wastes can serve here as an excellent source of organic carbon in microbiological processes.

It is well known that burning of hydrogen either chemically or electrochemically (e.g. fuel cells) generates large quantities of energy and it is environmentally friendly. Application of biohydrogen in local environment (farms, small communities, etc.) certainly will improve local energy distribution and will lower costs of used energy.

This review paper describes basic principles of fermentative and phofermentative hydrogen generation. Biophotolysis of water, anaerobic dark and photofermentative processes in presence of organic substances, as well as the hybrid systems used in microbiological methods of hydrogen generation are described. The description of the applied microorganisms and enzymes is presented.
